Powder, method of producing powder, and adsorption apparatus

ABSTRACT

The present invention provides that powder is mainly constituted from secondary particles of hydroxyapatite. The secondary particles are obtained by drying a slurry containing primary particles of hydroxyapatite and aggregates thereof and granulating the primary particles and the aggregates. A bulk density of the powder is 0.65 g/mL or more and a specific surface area of the secondary particles is 70 m 2 /g or more. The powder of the present invention has high strength and is capable of exhibiting superior adsorption capability when it is used for an adsorbent an adsorption apparatus has.

The present application is a Divisional application of U.S. applicationSer. No. 13/497,635, which is a National Stage of International PatentApplication No. PCT/JP2010/066350 filed Sep. 22, 2010, which claimspriority to Japanese Application No. 2009-223355 filed Sep. 28, 2009.The disclosures of U.S. application Ser. No. 13/497,635 andInternational Patent Application No. PCT/JP2010/066350 are incorporatedby reference herein in their entireties.

TECHNICAL FIELD

The present invention relates to powder, a method of producing powder,and an adsorption apparatus.

RELATED ART

Hydroxyapatite has high biocompatibility, high safety and the like. Forthese reasons, in recent years, the hydroxyapatite has been usedgenerally as a material for stationary phase of a chromatography whichis used when a bio medicine such as an antibody and a vaccine ispurified and isolated.

As described above, the hydroxyapatite is used as the material forstationary phase of the chromatography, which can be produced asfollows.

First, a first liquid containing calcium hydroxide is mixed with asecond liquid containing phosphoric acid to obtain a mixture. Then, thecalcium hydroxide is reacted with the phosphoric acid with stirring themixture to obtain a slurry containing primary particles ofhydroxyapatite and aggregates thereof. Next, the slurry containing theprimary particles and the aggregates thereof is dried. Then, the driedprimary particles and aggregates are granulated to thereby obtainsecondary particles (powder) of the hydroxyapatite.

Next, the powder is sintered to obtain sintered powder (hereinafter,referred to as “sintered powder”). The powder and the sintered powderare filled in a column (absorption apparatus) as a material forstationary phase (adsorbent) (see Patent Document 1).

In the reaction to obtain the hydroxyapatite by using such calciumhydroxide and phosphoric acid, by-products other than the hydroxyapatiteare only water. Therefore, there is an advantage that no by-productsremain in the formed powder and the sintered powder. Further, there isalso an advantage that the reaction is controlled with ease by adjustingpH of the first liquid and the second liquid. This is because thereaction is an acid-base reaction.

However, in such a method, the calcium hydroxide has low solubility tothe first liquid. Due to the fact, the reaction of the calcium hydroxideand phosphoric acid becomes a solid-liquid reaction. Therefore, theaggregates of the primary particles formed in the slurry are non-uniformin an agglomeration degree thereof.

If powder of hydroxyapatite is obtained by drying a slurry in a state ofthe non-uniform aggregates in such an agglomeration degree, there is aproblem in that the powder cannot obtain sufficient strength due to alow bulk density of the powder. Further, when the powder is used as amaterial for stationary phase, there is also a problem in that thematerial for stationary phase cannot exhibit superior adsorptioncapability because a specific surface area of particles of the powderbecomes low. In this regard, it is to be noted that a particle in thisspecification means each of particles (secondary particles) and powderin this specification means that a plurality of particles gatheredtogether.

In particular, such problems are caused more conspicuously when powderof particles having a particle size of 10 μm or less is used for thematerial for stationary phase.

In order to solve the problems, there is known a method of obtainingspherical hydroxyapatite particles by spraying a slurry ofhydroxyapatite into a plasma generation apparatus and then heating thesprayed slurry at a temperature of several thousand degree. However, insuch a method, phosphoric acid is volatilized at a high temperature sothat an amount of calcium becomes excess. Therefore, particles whichhave no apatite structure and do not have a constant composition areobtained. Such particles are not suitable as a material for stationaryphase.

The Patent document 1 is JP-A 03-218460.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide powder that has highstrength and is capable of exhibiting excellent adsorption capabilitywhen it is used for an adsorbent used in an adsorption apparatus.Furthermore, it is another object of the present invention to provide amethod of producing powder that can produce such powder and anadsorption apparatus that uses such powder as an adsorbent.

These objects are achieved by the present inventions (1) to (10)described below.

(1) Powder including hydroxyapatite, wherein the hydroxyapatite includesprimary particles and secondary particles obtained by drying a slurrycontaining the primary particles and aggregates thereof and granulatingthe primary particles and the aggregates, and the powder comprising:mainly the secondary particles of the hydroxyapatite, wherein a bulkdensity of the powder is 0.65 g/mL or more and a specific surface areaof the secondary particles is 70 m²/g or more.

The powder, which has the bulk density within such a range and theparticles having the specific surface area within such a range, has highstrength and are capable of exhibiting excellent adsorption capabilitywhen it is used for an adsorbent used in an adsorption apparatus.

(2) In the method described in the above-mentioned item (1), asphericity of each of the secondary particles of the powder is in therange of 0.95 to 1.00.

When the powder including the particles having high sphericity is usedas an adsorbent used in an adsorption apparatus, it is possible toimprove a filling ratio of the powder into an adsorbent filling space ofthe adsorption apparatus.

(3) In the method described in the above-mentioned item (1) or (2), thesecondary particles consisting the powder are classified so as to havean average particle size of 40±4 μm, wherein when a repose angle of thepowder constituted of the classified secondary particles is measured,the repose angle is 27° or lower.

The powder having a low repose angle has a high flowability. Therefore,when the powder is used as an adsorbent used in an adsorption apparatus,it is possible to improve a filling efficiency of filling the powderinto an adsorbent filling space of the adsorption apparatus.

(4) In the method described in the above-mentioned items (1) to (3), thepowder is sintered at a temperature of 700° C. to obtain sintered powderhaving particles, and then the particles of the sintered powder areclassified so as to have an average particle size of 40±4 μm, whereinwhen a compressive particle strength of the classified particles ismeasured, the compressive particle strength is over 9.0 MPa.

The powder comprised of the particles having the compressive particlestrength within such a range can have sufficiently strength when it isused as an adsorbent used in an adsorption apparatus.

(5) In the method described in the above-mentioned items (1) to (4), thepowder is sintered at a temperature of 700° C. to obtain sintered powderincluding particles each having a surface and micropores formed on thesurface, wherein an average pore size of the micropores is 0.07 μm orless.

This makes it possible to reliably increase the specific surface area ofthe particles of the sintered powder.

(6) In the method described in the above-mentioned items (1) to (5), anaverage particle size of the secondary particles of the powder is in therange of 2 to 100 μm.

The powder of the particles having such an average particle size ispreferably used to the present invention. When the powder is used for anadsorbent used in an adsorption apparatus, the powder exhibits highstrength and excellent adsorption capability.

(7) A method of producing the powder described in the above-mentioneditems (1) is provided. The method comprises: mixing a first liquidcontaining a calcium raw material with a second liquid containing aphosphoric raw material to obtain a mixture; reacting the calcium rawmaterial with the phosphoric raw material with stirring the mixture toobtain the slurry containing the primary particles of the hydroxyapatiteand the aggregates thereof; crushing the aggregates contained in theslurry physically to disperse crushed aggregates in the slurry; anddrying the slurry and granulating the crushed aggregates to obtain thepowder mainly constituted from the secondary particles of thehydroxyapatite.

This makes it possible to produce powder which is mainly constitutedfrom the secondary particles of the hydroxyapatite. The bulk density ofthe powder is 0.65 g/mL or more and the specific surface area of theparticles of the powder is 70 m²/g or more.

(8) In the method described in the above-mentioned item (7), thecrushing the aggregates physically is performed by a wet-type jet millmethod in which the slurry is sprayed under a high pressure to obtaindroplets of the slurry and the droplets are crashed to each other.

According to the method, it is possible to reliably crush the aggregatesof the primary particles of the hydroxyapatite. Therefore, it ispossible to reliably obtain powder which has a bulk density of 0.65 g/mLor more and particles having a specific surface area of 70 m²/g or more.

(9) In the method described in the above-mentioned item (7) or (8), anaverage particle size of the crushed aggregates is 1 μm or less.

By falling the average particle size of the crushed aggregates withinsuch an range, it is possible to reliably obtain powder which has a bulkdensity of 0.65 g/mL or more and particles having a specific surfacearea of 70 m²/g or more.

(10) An adsorption apparatus provided with the powder described in theabove-mentioned item (1) or sintered powder obtained by sintering thepowder as an adsorbent.

This makes it possible to obtain an adsorption apparatus having highreliability.

In the present invention, it is possible to produce powder which ismainly constituted of hydroxyapatite by drying a slurry containingprimary particles of the hydroxyapatite and then granulating the primaryparticles. The bulk density of the powder is 0.65 g/mL or more and thespecific surface area of the particles is 70 m²/g or more. Therefore,the powder has high strength and is capable of exhibiting excellentadsorption capability when it is used for an adsorbent used in anadsorption apparatus.

Further, according to the method of producing powder of the presentinvention, it is possible to reliably and easily produce the powderwhich has a bulk density of 0.65 g/mL or more and particles having aspecific surface area of 70 m²/g or more.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view which shows one example of an adsorptionapparatus to be used in the present invention.

FIG. 2 shows particle size distribution curves of aggregates containedin a slurry. FIG. 2 (a) shows a particle size distribution curve of theaggregates before crushing. FIG. 2 (b) shows a particle sizedistribution curve of the aggregates after crushing.

FIG. 3 shows electron microscope photographs of dried powders obtainedin Example 1 and Comparative Example 1.

FIG. 4 shows electron microscope photographs in the vicinities ofsurfaces of particles of dried powders obtained in Example 1 andComparative Example 1.

FIG. 5 shows micropore distribution curves in surfaces of particles ofsintered powders obtained in Example 1 and Comparative Example 1.

FIG. 6 shows electron microscope photographs of dried powders obtainedin Example 2 and Comparative Example 2.

FIG. 7 shows a particle size distribution curve of particles of driedpowder obtained in Example 2.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinbelow, powder, a method of producing powder, and an adsorptionapparatus according to the present invention will be described in detailwith reference to their preferred embodiments.

First, prior to the description of the powder and the method ofproducing the powder according to the present invention, one example ofan adsorption apparatus (separation apparatus) to be used in the presentinvention, namely the adsorption apparatus provided with the powderaccording to the present invention will be described.

FIG. 1 is a sectional view which shows one example of an adsorptionapparatus to be used in the present invention. It is to be noted that inthe following description, the upper side and the lower side in FIG. 1will be referred to as “inflow side” and “outflow side”, respectively.

More specifically, the inflow side means a side from which liquids suchas a sample solution (i.e., a liquid containing a sample) and an eluateare supplied into the adsorption apparatus to separate (purify) a targetmaterial to isolate, and the outflow side means a side located on theopposite side from the inflow side, that is, a side through which theliquids described above discharge out of the adsorption apparatus as adischarge liquid.

The adsorption apparatus 1 shown in FIG. 1, which is used for separating(isolating) the target material to isolate from the sample solution,includes a column 2, a granular adsorbent (filler) 3, and two filtermembers 4 and 5.

The column 2 is constituted from a column main body 21 and caps 22 and23 to be attached to the inflow-side end and outflow-side end of thecolumn main body 21, respectively.

The column main body 21 is formed from, for example, a cylindricalmember. Examples of a constituent material of each of the parts(members) constituting the column 2 including the column main body 21include various glass materials, various resin materials, various metalmaterials, and various ceramic materials and the like.

An opening of the column main body 21 provided on its inflow side iscovered with the filter member 4, and in this state, the cap 22 isthreadedly mounted on the inflow-side end of the column main body 21.Likewise, an opening of the column main body 21 provided on its outflowside is covered with the filter member 5, and in this state, the cap 23is threadedly mounted on the outflow-side end of the column main body21.

The column 2 having such a structure as described above has an adsorbentfilling space 20 which is defined by the column main body 21 and thefilter members 4 and 5, and at least a part of the adsorbent fillingspace 20 is filled with the adsorbent 3 (in this embodiment, almost theentire of the adsorbent filling space 20 is filled with the adsorbent3).

A volumetric capacity of the adsorbent filling space 20 is appropriatelyset depending on the volume of a sample solution to be used. Such avolumetric capacity is not particularly limited, but is preferably inthe range of about 0.1 to 100 mL, and more preferably in the range ofabout 1 to 50 mL per 1 mL of the sample solution.

By setting a size of the adsorbent filling space 20 to a value withinthe above range and by setting a size of the adsorbent 3 (which will bedescribed later) to a value within a range as will be described later,it is possible to selectively isolate (purify) the target material toisolate (isolation material) from the sample solution. In other words,it is possible to reliably separate the isolation material such as aprotein, an antibody and a vaccine from contaminating substances(foreign substances) other than the isolation material contained in thesample solution.

Further, liquid-tightness between the column main body 21 and the caps22 and 23 is ensured by attaching the caps 22 and 23 to the openings ofthe column main body 21.

An inlet pipe 24 is liquid-tightly fixed to the cap 22 at substantiallythe center thereof, and an outlet pipe 25 is also liquid-tightly fixedto the cap 23 at substantially the center thereof. The liquids describedabove are supplied to the adsorbent filling space 20 through the inletpipe 24 and the filter member 4. The liquids supplied to the adsorbentfilling space 20 pass through gaps between particles of the adsorbent 3and then discharge out of the column 2 through the filter member 5 andthe outlet pipe 25. At this time, the isolation material and thecontaminating substances other than the isolation material contained inthe sample solution (sample) are separated from each other based on adifference in degree of adsorption of each of the isolation material andthe contaminating substances with respect to the adsorbent 3 and adifference in degree of affinity of each of the isolation material andthe contaminating substances with respect to an eluate.

Each of the filter members 4 and 5 has a function of preventing theadsorbent 3 from discharging out of the adsorbent filling space 20.Further, each of the filter members 4 and 5 is formed of a nonwovenfabric, a foam (a sponge-like porous body having communicating pores), awoven fabric, a mesh or the like, which is made of a synthetic resinsuch as polyurethane, polyvinyl alcohol, polypropylene,polyetherpolyamide, polyethylene terephthalate, or polybutyleneterephthalate.

In the present embodiment, the adsorbent 3 used to the adsorptionapparatus 1 is constituted of the powder of the present invention(secondary particles of hydroxyapatite) or sintered powder thereof.

The powder of present invention is obtained by drying a slurrycontaining primary particles of hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) andaggregates thereof, and granulating them. The particles of the powderare mainly constituted of the hydroxyapatite. It is characterized inthat a bulk density of the powder is 0.65 g/mL or more and a specificsurface area of the particles of the powder is 70 m²/g or more. Thehydroxyapatite is constituted from a chemically stable apatitestructure. The hydroxyapatite is reliably used for the adsorbent whichis provided with the adsorption apparatus. In this regard, it isintended that a Ca/P ratio of the hydroxyapatite is in the range ofabout 1.64 to 1.70.

When the sample solution is supplied into the adsorption apparatus 1which has the adsorbent 3, the separation material contained in thesample solution is specifically adsorbed to the adsorbent 3 withinherent adsorbability (carrying power) of the separation material.Then, the separation material is separated from the contaminatingsubstances other than the separation material contained in the samplesolution according to a difference between the adsorbalilities of theseparation material and contaminating substances with respect to theadsorbent 3, and thus is purified.

As described above, the bulk density of secondary particles (powder) ofthe hydroxyapatite may be 0.65 g/mL or more, and more preferably is inthe range of about 0.70 to 0.95 g/mL or more. It is considered that thesecondary particles having the bulk density within such a range have aheavy weight and gaps in the particle are lowered. In other words, thesecondary particles can exhibit high strength because the secondaryparticles have a high filling density. Therefore, when the secondaryparticles are used as the adsorbent 3, it is possible to assist a longlife of the adsorbent 3.

As described above, the specific surface area of the particles of thepowder may be 70 m²/g or more, and more preferably is in the range ofabout 75 to 100 m²/g. The powder which is constituted of the particleshaving a high specific surface area within such a range makes itpossible to increase an opportunity to make the isolation materialcontact with the adsorbent 3, thereby improving interaction between theisolation material and adsorbent 3, when the powder is used as theadsorbent 3. Therefore, the adsorbent 3 exhibits excellent adsorptioncapability with respect to the isolation material.

Here, particles of powder having a high bulk density, generally, have alow specific surface area. However, in the powder of the presentinvention, the bulk density is 0.65 g/mL or more and the specificsurface area of the particles is 70 m²/g or more. Thus, it becomesrealizable to change the bulk density to a high bulk density and thespecific surface area to a large specific surface area. It is consideredto be caused by that both the bulk density of the powder and thespecific surface area of the secondary particles are improved. The gapsin the secondary particle are reduced. In contrast, it is caused thatfine pores and fine irregularities are formed in the vicinities of thesurfaces of the secondary particles. It is considered that it is a mainfactor that the primary particles of the hydroxyapatite have a finecolumnar shape, and the primary particles having the fine columnar shapecomplicatedly intervene with each other. On the other hand, gaps betweenthe primary particles tend to be too large in primary particles havingan indefinite shape, a plate shape and a spherical shape, so that it isdifficult to maintain both the high bulk density and the large specificsurface area.

Further, a form (shape) of the secondary particles, namely the adsorbent3 is preferably a granulated shape (granular shape) as shown in FIG. 1.A sphericity of each of the secondary particles is preferably in therange of about 0.95 to 1.00 and more preferably in the range of about0.97 to 1.00. When the secondary particles having a high sphericity asdescribed above are used as the adsorbent 3, it is possible to improvethe filling ratio of the adsorbent 3 into the adsorbent filling space20.

A repose angle of such powder (secondary particles) is preferably 27° orlower and more preferably in the range of about 25 to 22° when such arepose angle is measured by using the secondary particles classified toan average particle size in the range of 40±4 μm. The secondaryparticles of the powder having such a low repose angle have highflowability and can assist the improvement of the operability (fillingefficiency) when the secondary particles are filled into the adsorbentfilling space 20 as the adsorbent 3.

Further, in sintered powder obtained by sintering the secondaryparticles, in the case where the secondary particles are sintered at atemperature of 700° C., an average pore size of micropores formed on thesurface thereof is preferably 0.07 μm or less, and more preferably inthe range of about 0.04 to 0.06 μm. Further, in the case where thesecondary particles are sintered at the temperature of 400° C., theaverage pore size of the micropores is preferably 0.05 μm or less, andmore preferably in the range of about 0.02 to 0.04 μm. By falling theaverage pore size of the micropores within the range, it is possible toreliably improve the specific surface area of the particles of thesintered powder.

Such secondary particles are classified to the average particle size inthe range of 40±4 μm. A compressive particle strength (breakingstrength) of the classified secondary particles (powder) is preferably2.0 MPa or larger, and more preferably in the range of about 2.4 to 3.0MPa.

Furthermore, in the case where the sintered powder obtained by sinteringthe secondary particles is classified to the average particle size inthe range of 40±4 μm and the secondary particles are sintered at thetemperature of 700° C., a compressive particle strength (breakingstrength) of the classified particles of the sintered powder ispreferably 9 MPa or larger, and more preferably in the range of about9.4 to 10 MPa. Further, in the case where the secondary particles aresintered at the temperature of 400° C., a compressive particle strengthof the particles is preferably 7.0 MPa or larger, and more preferably inthe range of about 7.3 to 8.0 MPa.

The powder and the sintered powder each having the compressive particlestrength within such a range have enough strength to be used for theadsorbent 3.

Further, an average particle size of the secondary particles is notparticularly limited, but is preferably in the range of about 2 to 100μm, more preferably in the range of about 2 to 80 μm, and even morepreferably in the range of about 3 to 10 μm. The secondary particleshaving such an average particle size are reliably used for the presentinvention. When the secondary particles are used for the adsorbent 3,the secondary particles can exhibit high strength and superioradsorption capability.

In this regard, in addition to the case where almost the entire of theadsorbent filling space 20 is filled with the adsorbent 3 as thisembodiment, it is to be noted that the adsorbent filling space 20 of theadsorption apparatus of the present invention may be partially filledwith the adsorbent 3 (e.g., a part of the adsorbent filling space 20located on its one side where the inlet pipe 24 is provided may befilled with the adsorbent 3). In this case, the remaining part of theadsorbent filling space 20 may be filled with another adsorbent.

The powder of the present invention as described above can be producedby the method of producing the powder of the present invention asfollows.

In the method of producing the powder of the present invention, a firstliquid containing a calcium raw material such as calcium hydroxide as acalcium source is mixed with a second liquid containing a phosphate rawmaterial such as phosphoric acid as a phosphoric source to obtain amixture. The calcium raw material is reacted with the phosphate rawmaterial with stirring the mixture to obtain a slurry containing primaryparticles of hydroxyapatite and aggregates thereof. These operations arereferred to as a first step [S1]. Next, the aggregates contained in theslurry are crushed physically, so that the crushed aggregates aredispersed in the slurry. This operation is referred to as a second step[S2]. Finally, the slurry is dried, and then the crushed aggregates aregranulated to obtain powder which is mainly constituted from secondaryparticles of the hydroxyapaite. This operation is referred to as a thirdstep [S3].

Hereinafter, these steps will be described one after another.

In this regard, the following descriptions will be made on an example ofthat calcium hydroxide is used as the calcium source and phosphoric acidis used as the phosphoric source.

[S1: Step of Obtaining Slurry Containing Aggregates of Hydroxyapatite(First Step)]

In this step, a calcium hydroxide dispersion liquid containing calciumhydroxide (first liquid) is mixed with a phosphoric acid aqueoussolution containing phosphoric acid (second liquid) to obtain themixture. The calcium hydroxide is reacted with the phosphoric acid withstirring the mixture to obtain the slurry containing the aggregates ofthe primary particles of hydroxyapatite.

To be concrete, the phosphoric acid aqueous solution (second liquid) isdropped into the calcium hydroxide dispersion liquid (first liquid) in avessel (not shown) while the calcium hydroxide dispersion liquid isstirred. By doing so, the mixture of the calcium hydroxide dispersionliquid and the phosphoric acid aqueous solution are prepared.Thereafter, the calcium hydroxide is reacted with the phosphoric acid inthe mixture to obtain the slurry containing the aggregates of thehydroxyapatite.

In this process, used is a wet synthesis method that the phosphoric acidis used as a aqueous solution. This makes it possible to efficiently andeasily synthesize hydroxyapatite (synthetic material) without use of anexpensive production facility. Further, in the reaction of the calciumhydroxide and the phosphoric acid, by-products other than hydroxyapatiteare only water. Therefore, there is an advantage that no by-product sremain in the secondary particles of the hydroxyapatite and the sinteredpowder to be formed. Since this reaction is an acid-base reaction, thereis also an advantage that the reaction is controlled with ease byadjusting pH of the calcium hydroxide dispersion liquid and thephosphoric acid aqueous solution.

By performing this reaction with stirring the mixture, it is possible toefficiently perform the reaction between the calcium hydroxide and thephosphoric acid. In other words, it is possible to improve efficiency ofthe reaction therebetween.

Furthermore, power for stirring (stirring power) the mixture containingthe phosphoric acid aqueous solution and the calcium hydroxidedispersion liquid is not particularly limited to a specific power, butpreferably in the range of about 0.75 to 2.0 W and more preferably inthe range of about 0.925 to 1.85 W per 1 L of the mixture (slurry). Bysetting the stirring power to a value within the above range, it ispossible to further improve the efficiency of the reaction between thecalcium hydroxide and the phosphoric acid.

A content of the calcium hydroxide in the calcium hydroxide dispersionliquid is preferably in the range of about 5 to 15 wt % and morepreferably in the range of about 10 to 12 Wt %. A content of thephosphoric acid in the phosphoric acid aqueous solution is preferably inthe range of about 10 to 25 wt % and more preferably in the range ofabout 15 to 20 Wt %. By setting the contents of the calcium hydroxideand the phosphoric acid to values within the above ranges, respectively,it is possible to efficiently react the calcium hydroxide and thephosphoric acid. Consequently, it is possible to reliably synthesizehydroxyapatite. This is because an opportunity of contacting between thecalcium hydroxide and the phosphoric acid increases when the phosphoricacid aqueous solution is dropped into the calcium hydroxide dispersionliquid with stirring the calcium hydroxide dispersion liquid.

A rate of dropping the phosphoric acid aqueous solution into the calciumhydroxide dispersion liquid is preferably in the range of about 1 to 40L/hr and more preferably in the range of about 3 to 30 L/hr. By mixing(adding) the phosphoric acid aqueous solution with (to) the calciumhydroxide dispersion liquid at such a dropping rate, it is possible toreact calcium hydroxide with phosphoric acid under milder conditions.

In this case, the phosphoric acid aqueous solution is preferably dropped(added) into (to) the calcium hydroxide dispersion liquid for a lengthof time from about 5 to 32 hours, and more preferably for a length oftime from about 6 to 30 hours. By dropping the phosphoric acid aqueoussolution into the calcium hydroxide dispersion liquid in such a periodof time to react the calcium hydroxide with the phosphoric acid, it ispossible to sufficiently synthesize hydroxyapatite. It is to be notedthat even if the time for dropping the phosphoric acid aqueous solutioninto the calcium hydroxide dispersion liquid is prolonged to exceed theabove upper limit value, it cannot be expected that the reaction betweenthe calcium hydroxide and the phosphoric acid will further proceed.

When the reaction between the calcium hydroxide and the phosphoric acidgradually proceeds, fine particles of hydroxyapatite (syntheticmaterial) (hereinafter, simply referred to as “fine particles”) areproduced in the slurry. A chemical structure of such fine particlesincludes positively-charged parts and negatively-charged parts.Therefore, Van der Waals' forces (intermolecular force) are made betweenthe positively-charged parts in the chemical structure of one fineparticle of the fine particles and the negatively-charged parts in thechemical structure of the other fine particle of the fine particles. Bythis Van der Waals' forces, the one fine particle and the other fineparticle adhere to each other to obtain a pre-aggregate. Then, in thesurly, pre-aggregates are agglutinated to obtain aggregates ofhydroxyapatite (synthetic material) (hereinafter, simply referred to as“aggregates”). The aggregates make a viscosity of the slurry increasegradually.

When the reaction between the calcium hydroxide and the phosphoric acidfurther proceeds, a ratio between the positively-charged parts and thenegatively-charged parts of the fine particles contained in the slurrytends to approach each other. At this time, in the slurry, occurs aphenomenon that repulsive force occurring among the fine particles isreduced and the aggregation among fine particles further proceeds. As aresult, aggregates having more a large particle size are formed.

[S2: Step of Dispersing Crushed Aggregates after Crushing Aggregates(Second Step)]

In this step, the aggregates of the primary particles of hydroxyapatitecontained in the slurry obtained in the above step [S1] are physicallycrushed. Then, the crushed aggregates are dispersed in the slurry.

When the aggregates contained in the slurry are crushed, a particle sizeof each of the aggregates contained in the slurry is lowered. Due to thefact, in powder (secondary particles) of hydroxyapatite which will beobtained in a later step [S3], a bulk density thereof becomes 0.65 g/mLor more and a specific surface area of the secondary particles is 70m²/g or more.

A method of physically crushing the aggregates of the primary particlesof hydroxyapatite is not particularly limited, but examples thereofinclude a wet-type jet mill method, a ball mill method and the like. Thewet-type jet mill method includes steps of spraying a slurry under highpressure to obtain droplets of the slurry and crashing the droplets toeach other. The ball mill method includes steps of placing the slurryinto a closed vessel with spherical objects constituted of ceramics suchas zirconia and rotating the closed vessel. Among them, it is preferredthat the wet-type jet mill method is used.

Here, the wet-type jet mill method is a method as follows: First, highpressure is added to the slurry in which the aggregates of the primaryparticles of hydroxyapatite are dispersed. Next, by spraying the slurry,the slurry is introduced into an opposing crash chamber, a ball crashchamber or a single nozzle chamber in a state of droplets of the slurry.By doing so, the droplets of the slurry are crashed to each other tocrush the aggregates.

According to the method, the aggregates of the primary particles ofhydroxyapatite are crushed reliably. Therefore, it is possible toreliably obtain powder (secondary particles) of hydroxyapatite whichwill be obtained in a later step [S3] so that the bulk density of thepowder is 0.65 g/mL or more and the specific surface area of thesecondary particles is 70 m²/g or more.

An average particle size of the crushed aggregates is preferably 1 μm orless and more preferably in the range of about 0.1 to 0.6 μm. By fallingthe average particle size of the crushed aggregates within such a range,it is possible to reliably fall the bulk density of the powder(secondary particles) of hydroxyapatite which will be obtained in thelater step [S3] and the specific surface area of the secondary particleswithin the ranges.

In this regard, a method of adding a surfactant or a dispersant todisperse the primary particles into the slurry may be used as the methodof dispersing the primary particles into the slurry other than themethod of physically crushing the aggregates of the primary particles asthis embodiment. However, in the former method (method of adding thesurfactant or the dispersant), the added surfactant or dispersantremains in the powder of hydroxyapatite during a step of drying theslurry in the later step [S3]. Therefore, in order to remove them, it isneeded that the powder of hydroxyapatite is sintered at a temperature of800° C. or higher. When the powder is sintered at such a temperature, aspecific surface area of the particles of the powder is lowered.Therefore, it is substantially impossible for the former method to setthe specific surface area of the particles to 70 m²/g or more as thepowder of the present invention.

[S3: Step of Obtaining Powder of Hydroxyapatite by Drying Slurry (ThirdStep)]

In this step, the slurry containing the aggregates crushed and obtainedin the above step [S2] is dried and then the crushed aggregates isgranulated, so that powder (dried powder) mainly constituted from thesecondary particles of hydroxyapatite is obtained.

In the present invention, the aggregates in which the primary particlesof hydroxyapatite are aggregated are crushed to obtain aggregates of asmall size in the above step [S2]. Therefore, in the powder ofhydroxyapatite obtained in the present step [S3], a bulk density thereofbecomes 0.65 g/mL or more and a specific surface area of the particlesbecomes 70 m²/g or more.

A method of drying the slurry is not particularly limited to a specificmethod, but a spray drying method is preferably used. According to sucha method, it is possible to reliably obtain powder including particleshaving a predetermined particle size for a short period of time bygranulating the crushed aggregates.

Further, a drying temperature of the slurry is preferably in the rangeof about 75 to 250° C. and more preferably in the range of about 95 to220° C. By setting the drying temperature to a value within the aboverange, it is possible to obtain powder which has a high bulk density andthe secondary particles having a large specific surface area.

The method of producing the powder according to the present embodiment,in particular, is suitable to produce powder containing particles havingan intended particle size in the range of about 2 to 100 μm (inparticular, about 3 to 10 μm).

In this regard, it is to be noted that such powder (dried powder) can besintered to obtain sintered powder. This makes it possible to improvecompressive particle strength (breaking strength) of the particles ofthe powder (sintered powder).

In this case, a sintering temperature of the powder is preferably in therange of about 200 to 900° C. and more preferably in the range of about400 to 700° C.

By completing the steps as described above, it is possible to obtainpowder constituted of the secondary particles of hydroxyapatite(synthetic material).

Although the powder, the method of producing the powder and theadsorption apparatus according to the present invention have beendescribed above, the present invention is not limited thereto.

For example, the method of producing the powder according to the presentinvention may further include a pre-step before the step [S1], anintermediate step between the step [S1] and the step [S2] or between thestep [S2] and the step [S3], and a post-step after the step [S3] for anypurpose.

EXAMPLES

Next, the present invention will be described with reference to actualexamples.

1. Production of Hydroxyapatite Having Particle Size of 40 μm Example 1

[1A] First, calcium hydroxide of 2400 g was dispersed in pure water of60 L to obtain a calcium hydroxide dispersion liquid. Then, the calciumhydroxide dispersion liquid was added into a tank. An phosphoric acidaqueous solution (phosphoric acid concentration is 85 wt %) of 4 L wasdropped into the calcium hydroxide dispersion liquid at a speed of 1L/hr while the calcium hydroxide dispersion liquid was stirred in thetank. As a result, was obtained a slurry containing aggregates in whichprimary particles of hydroxyapatite of 10 wt % were aggregated.

In this regard, it is to be noted that an ambient temperature during thedropping process was set to normal temperature (25° C.)

Furthermore, a stirring power of the slurry in which the phosphoric acidaqueous solution was dropped into the calcium hydroxide dispersionliquid was set to 1.7 W with respect to 1 L of the slurry.

[2A] Next, the aggregates contained in the obtained slurry were crushedunder high pressure of 200 MPa by using a wet-type jet mill apparatus(“StarBurst” produced by SUGINO MACHINE LIMITED), to thereby obtain aslurry containing the crushed aggregates.

A particle size distribution curve of each of the aggregates containedin the slurry before crushing and the aggregates contained in the slurryafter crushing was measured by using a particle size distributionanalyzer (“MT3300” produced by Microtrac).

The results are shown in FIG. 2(a) and FIG. 2(b).

As clearly shown from FIG. 2(b), the aggregates contained in the slurrycould be crushed by using the wet-type jet mill apparatus. Concretely,it found that the aggregates could be crushed by an average particlesize of 0.74 μm.

[3A] Next, the slurry containing the crushed aggregates was spray-driedat a temperature of 210° C. using a spray drier (“MAD-6737R”manufactured by MATSUBO Corporation) to thereby granulate hydroxyapatitecontained in the slurry. In this way, particulate secondary particles(dried powder) were obtained. Thereafter, the thus obtained secondaryparticles (dried powder) (hydroxyapatite powder) were classified byusing a cyclone classifier (“TC-15” produced by NISSHIN ENGINEERINGINC.) to obtain particles having a median particle size of about 40 μm.

In this regard, it is to be noted that the thus obtained powder(secondary particles) was confirmed to be hydroxyapatite by a powderX-ray diffractometry.

[4A] Next, a part of the classified dried powder (secondary particles)was sintered at sintering temperatures of 400° C. and 700° C. to obtainsintered powders.

Comparative Example 1

Secondary particles of hydroxyapatite having a median particle size ofabout 40 μm (dried powder) and sintered powders thereof were obtained inthe same manner as in the Example 1, except that the above step [2A],namely the step of crushing the aggregates contained in the slurry wasomitted.

2. Evaluation of Hydroxyapatite Having Particle Size of 40 μm 2-1.Evaluation of Bulk Densities of Dried Powder and Sintered Powders

Each of the dried powders (secondary particles) and the sintered powderssintered at the sintering temperatures of 400° C. and 700° C., whichwere obtained in the Example 1 and the Comparative Example 1, werefilled into a stainless tube of 1.256 mL by tapping it 100 times. Then,their bulk densities were obtained by measuring their filling amounts,respectively.

The results are shown in Table 1.

TABLE 1 Table 1 Bulk densities [g/mL] Dried Sintered particles Sinteredparticles powder (400° C.) (700° C.) Ex. 1 0.70 0.70 0.70 Com. Ex. 10.63 0.63 0.63

As clearly seen from Table 1, the bulk densities of the dried powder andthe sintered powders obtained in the Example 1 were improved by about10% as compared with the bulk densities of the dried powder and thesintered powders obtained in the Comparative Example 1. From theseresults, it is considered that not only gaps in the particle of theformed dried powder but also gaps in the particle of the formed sinteredpowders became small by crushing the aggregates of their primaryparticles contained in the slurry, so that a filling density in the tubebecame high.

2-2. Evaluation of Specific Surface Areas of Particles of Dried Powderand Sintered Powders

Each of the dried powders (secondary particles) and the sintered powderssintered at the sintering temperatures of 400° C. and 700° C., whichwere obtained in the Example 1 and the Comparative Example 1, weresubjected to an automatic BET specific surface area analyzer (“MacsorbHM1201” produced by Mountech Co., Ltd) to obtain a specific surface areaof the particles thereof.

The results are shown in Table 2.

TABLE 2 Table 2 Specific surface areas [m²/g] Sintered particlesSintered particles Dried powder (400° C.) (700° C.) Ex. 1 75 52 25 Com.Ex. 1 60 40 20

As clearly seen from Table 2, the specific surface areas of theparticles of the dried powder and the sintered powders obtained in theExample 1 were improved as compared with the specific surface areas ofthe particles of the dried powder and the sintered powders obtained inthe Comparative Example 1. This tendency, in particular, was confirmedconspicuously in the dried powder.

Generally, if conditions of surfaces of particles are identical to eachother, is shown a tendency that a specific surface area of particles ofpowder having a high bulk density is smaller than that of particles ofpowder having a low bulk density. However, as shown in the above item“2-1. Evaluation of Bulk Densities”, both the bulk densities and thespecific surface areas of the dried powder and the sintered powdersobtained in the Example 1 were improved as compared with the bulkdensities and the specific surface areas of the dried powder and thesintered powders obtained in the Comparative Example 1. From theseresults, it is considered that fine pores are formed in the surfaces ofthe particles of the dried powder and the sintered powders obtained inthe Example 1 or their surfaces are irregularity formed due to the crushof the aggregates of their primary particles contained in the slurry. Asa result, it is considered that the specific surface areas of theparticles of their powders are also improved regardless of theimprovement of the bulk densities of their powders.

2-3. Evaluation of Sphericities of Particles of Dried Powder andSintered Powders

Each of the dried powders (secondary particles) and the sintered powderssintered at the sintering temperatures of 400° C. and 700° C., whichwere obtained in the Example 1 and the Comparative Example 1, weresubjected to a flow particle image analyzer (“FPIA-3000” produced bySYSMEX CORPORATION) to obtain a sphericity of the particles thereof.

The results are shown in Table 3.

Further, electron microscope photographs of the particles of the driedpowders obtained in the Example 1 and the Comparative Example 1 areshown in FIG. 3.

TABLE 3 Table 3 Sphericities Sintered particles Sintered particles Driedpowder (400° C.) (700° C.) Ex. 1 0.97 0.97 0.97 Com. Ex. 1 0.95 0.950.95

As clearly seen from Table 3, the sphericities of the particles of thedried powder and the sintered powders obtained in the Example 1 wereimproved as compared with the sphericities of the particles of the driedpowder and the sintered powders obtained in the Comparative Example 1.Further, as clearly seen from the electron microscope photographs inFIG. 3, the sphericity of each particle of the dried powder obtained inthe Example 1 was higher than the sphericity of each particle of thedried powder obtained in the Comparative Example 1. In addition to that,each surface of the particles of the dried powder obtained in theExample 1 was smooth.

2-4. Evaluation of Micropores of Surfaces of Particles of Dried Powderand Sintered Powders

Electron microscope photographs in the vicinities of the surfaces of theparticles of the dried powders obtained in the Example 1 and theComparative Example 1 are shown in FIG. 4.

As clearly seen from the electron microscope photographs in FIG. 4, itfound that the surfaces of the particles of the dried powder obtained inthe Comparative Example 1 were uneven. Further, sizes of the micropores,which were formed by vaporization of water during the step of spraydrying, were non-uniform. In contrast, the surfaces of the particles ofthe dried powder obtained in the Example 1 were smooth. In addition tothat, the micropores having substantially an uniform size weredistributed uniformly.

Each of the sintered powders sintered at the sintering temperatures of400° C. and 700° C. and obtained in the Example 1 and the ComparativeExample 1 was subjected to a pore size analyzer (“Micromeritics AutoPore9200” produced by Shimadzu Corporation). Then, micropore distributioncurves in the surfaces of the particles of each of the sintered powderswere measured by using a mercury intrusion technique.

The results are shown in FIG. 5.

As clearly seen from FIG. 5, it found that the sizes of the microporesin the surfaces of the particles of the sintered powders obtained in theExample 1 were uniform and small as compared with those in the surfacesof the particles of the sintered powders obtained in the ComparativeExample 1.

2-5. Evaluation of Repose Angles of Dried Powder and Sintered Powders

Each of the dried powders (secondary particles) and the sintered powderssintered at the sintering temperatures of 400° C. and 700° C., whichwere obtained in the Example 1 and the Comparative Example 1, weresubjected to a multi tester (“MT-1001” produced by SEISHIN ENTERPRISECO., LTD.) to obtain repose angles of the powders.

The results are shown in Table 4.

TABLE 4 Table 4 Repose angles [°] Sintered particles Sintered particlesDried powder (400° C.) (700° C.) Ex. 1 26 24 22 Com. Ex. 1 32 30 28

As clearly seen from Table 4, the repose angles of the dried powder andthe sintered powders obtained in the Example 1 were lower than those ofthe dried powder and the sintered powders obtained in the ComparativeExample 1. This reflected the results that the sphericities of theparticles of the dried powder and the sintered powders obtained in theExample 1 were higher than those of the particles of the dried powderand the sintered powders obtained in the Comparative Example 1, inaddition to that, the surfaces of the particles of the dried powderobtained in the Example 1 were smooth in the above item “2-3. Evaluationof Sphericities of Particles”.

2-6. Evaluation of Compressive Particle Strengths of Particles of DriedPowder and Sintered Powders

Each of the dried powders (secondary particles) and the sintered powderssintered at the sintering temperatures of 400° C. and 700° C., whichwere obtained in the Example 1 and the Comparative Example 1, weresubjected to a compression testing machine (“MCT-W200-J” manufactured byShimadzu Corporation) to obtain compressive particle strengths of theparticles thereof.

The results are shown in Table 5.

TABLE 5 Table 5 Compressive particle strengths [MPa] Sintered particlesSintered particles Dried powder (400° C.) (700° C.) Ex. 1 2.4 7.3 9.4Com. Ex. 1 2.2 3.2 2.7

As clearly seen from Table 5, the compressive particle strengths of thedried powder and the sintered powders obtained in the Example 1 becamehigher than those of the dried powder and the sintered powders obtainedin the Comparative Example 1. This reflected the results that the bulkdensities of the dried powder and the sintered powders obtained in theExample 1 became higher than those of the dried powder and the sinteredpowders obtained in the Comparative Example 1 in the above item “2-1.Evaluation of Bulk Densities”.

2-7. Results

As described above, it found both the bulk densities of the dried powderand the sintered powders to be formed and the specific surface areas oftheir particles were improved by crushing the aggregates contained inthe slurry, thereby lowering the particle size of the aggregates in theabove step [2A].

As described above, it found each of the dried powder and the sinteredpowders obtained in the Example 1 of which bulk densities were improvedexhibited (had) superior particle strength to the dried powder and thesintered powders obtained in the Comparative Example 1 from the resultsof the above item “2-6. Evaluation of Compressive Particle Strengths”.

Further, from the data obtained in the above item “2-2. Evaluation ofSpecific Surface Areas of Particles”, a surface area of the particlesper 1 mL of a column was obtained. The results are shown in Table 6. Thesurface areas of the particles of the dried powder and the sinteredpowders obtained in the Example 1 were about 1.2 to 1.4 times largerthan those of the particles of the dried powder and the sintered powdersobtained in the Comparative Example 1. In addition to that, amounts ofadsorbing materials were also about 1.2 to 1.4 times larger than thoseof the Comparative Example 1. From the results, it was considered thatadsorption properties of the particles of the dried powder and thesintered powders obtained in the Example 1 were improved.

TABLE 6 Table 6 Surface areas [mm²/mL] Sintered particles Sinteredparticles Dried powder (400° C.) (700° C.) Ex. 1 75 36.4 17.0 Com. Ex. 165 25.2 12.6

Further, the sphericities of the particles of the dried powder and thesintered powders obtained in the Example 1 were higher than those of theparticles of the dried powder and the sintered powders obtained in theComparative Example 1. In addition to that, the surfaces of theparticles of the dried powder and the sintered powders obtained in theExample 1 were smooth. Due to the results, the repose angles of thedried powder and the sintered powders obtained in the Example 1 becamelow. From these results, it is considered that it is possible to improveoperability in filling each of the dried powder and the sintered powdersobtained in the Example 1 into a filling space of a column.

3. Production of Hydroxyapatite Having Particle Size of 10 μm or LessExample 2

[1B] First, was obtained a slurry containing aggregates which wereformed by aggregating primary particles of hydorxyapatite of 10 wt % inthe same manner as in the above step [1A].

[2A] Next, the aggregates contained in the obtained slurry were crushedby using a wet-type jet mill apparatus in the same manner as in theabove step [2A]. As a result, a slurry containing the crushed aggregateswas obtained.

[3B] Next, the slurry containing the crushed aggregates was spray-driedat a temperature of 110° C. by using a small spray drier (“Mobile MinorSpray Dryer” manufactured by Niro Inc., a spray system is a twin-fluidatomizing system, a tip flow path is 300 μm). Then, hydroxyapatitecontained in the slurry was granulated to obtain particulate secondaryparticles (dried powder).

Comparative Example 2

Secondary particles of hydroxyapatite (dried powder) were obtained inthe same manner as in the Example 2, except that the above step [2B],namely the step of crushing the aggregates contained in the slurry wasomitted.

4. Evaluation of Hydroxyapatite Having Particle Size of 10 μm or Less

Electron microscope photographs of the dried powders obtained in theExample 2 and the Comparative Example 2 are shown in FIG. 6.

The dried powder obtained in the Example 2 had particles having a highsphericity and had a particle size distribution curve as shown in FIG.7. In addition to that, it was not confirmed that particles having alarge particle size of 30 μm or larger were mixed in the dried powderobtained in the Example 2.

In contrast, the sphericity of the particles of the dried powderobtained in the Comparative Example 2 was clearly lower than that of theparticles of the dried powder obtained in the Example 2. Furthermore,many particles having the particle size of 30 μm or larger were mixed inthe dried powder obtained in the Comparative Example 2. That is, it wasdifficult to obtain particles having the particle size of 10 μm or lessbecause the aggregates in themselves were aggregated in a particle sizeof a few dozen μm.

From the reasons described above, it found that it is possible to formeven the dried powder (secondary particles) of the particles of thehydroxyapatite having the particle size of 10 μm or less with the highsphericity and the uniform particle size by crushing the aggregatescontained in the slurry to lower the particle size of the aggregates inthe above step [2B].

INDUSTRIAL APPLICABILITY

The powder according to the present invention is mainly constituted fromthe secondary particles of the hydroxyapatite obtained by drying slurrycontaining the primary particles of the hydroxyapatite and theaggregates thereof, and then granulating the primary particles and theaggregates. The bulk density of the powder is 0.65 g/mL or more and thespecific surface area of the secondary particles is 70 m²/g or more.Therefore, the powder according to the present invention has the highstrength and is capable of exhibiting the excellent adsorptioncapability when it is used for the adsorbent the adsorption apparatushas. Accordingly, the powder according to the present invention hasindustrial applicability.

What is claimed is:
 1. A method of producing powder including secondaryparticles mainly formed of hydroxyapatite, the method comprising: mixinga first liquid containing a calcium source to be a raw material of thehydroxyapatite with a second liquid containing a phosphoric source to bethe raw material of the hydroxyapatite to obtain a mixture; reacting thecalcium source with the phosphoric source with stirring the mixture toobtain a slurry containing primary particles of the hydroxyapatite andaggregates thereof; physically crushing the aggregates contained in theslurry to disperse the crushed aggregates in the slurry; and granulatingthe primary particles and the crushed aggregates by spraying and dryingthe slurry to obtain the secondary particles.
 2. The method as claimedin claim 1, wherein power for stirring the mixture is in the range of0.75 to 2.0 W per 1 L of the mixture.
 3. The method as claimed in claim1, wherein a content of the calcium source in the first liquid is in therange of 5 to 15 wt % and a content of the phosphoric source in thesecond liquid is in the range of 10 to 25 wt %.
 4. The method as claimedin claim 1, wherein the mixing the first liquid with the second liquidis performed by dropping the second liquid into the first liquid at arate of 1 to 40 L/hour.
 5. The method as claimed in claim 4, wherein atime for dropping the second liquid into the first liquid is in therange of 5 to 32 hours.
 6. The method as claimed in claim 1, wherein thephysically crushing the aggregates is performed by a wet-type jet millmethod in which the slurry is sprayed under a high pressure to obtaindroplets of the slurry and the droplets are crashed to each other. 7.The method as claimed in claim 1, wherein the physically crushing theaggregates is performed by a ball mill method in which the slurry isplaced into a closed vessel together with spherical objects constitutedof ceramics, and then the closed vessel is rotated.
 8. The method asclaimed in claim 1, wherein the physically crushing the aggregates isperformed such that an average particle size of the crushed aggregatesis 1 μm or less.
 9. The method as claimed in claim 1, wherein thephysically crushing the aggregates is performed such that an averageparticle size of the crushed aggregates is in the range of 0.1 to 0.74μm.
 10. The method as claimed in claim 1, wherein an average particlesize of the secondary particles is in the range of 2 to 100 μm.
 11. Themethod as claimed in claim 1, wherein an average particle size of thesecondary particles is in the range of 3 to 10 μm.
 12. The method asclaimed in claim 1, wherein a bulk density of the powder is 0.65 g/mL ormore and a specific surface area of the secondary particles is 70 m²/gor more.